Fluidic device and method for separation of neutrally buoyant particles

ABSTRACT

A technique using a curved channel of a spiral device to introduce a centrifugal force upon neutrally buoyant particles flowing in a fluid, e.g. water, to facilitate improved separation of such particles from the fluid is provided. As these neutrally buoyant particles flow through the channel, a tubular pinch effect causes the particles to flow in a tubular band. The introduced centrifugal force perturbs the tubular band (e.g. forces the tubular band to flow in a manner offset from a center of the channel), resulting in an asymmetric inertial migration of the band toward the inner wall of the channel. This allows for focusing and compaction of suspended particulates into a narrow band for extraction. The separation principle contemplated herein implements a balance of the centrifugal and fluidic forces to achieve asymmetric inertial equilibrium near the inner sidewall.

CROSS REFERENCE TO RELATED PATENTS AND APPLICATIONS

This application is related to co-pending, commonly assigned U.S. patentapplication Ser. No. 11/606,460, filed Nov. 30, 2006, entitled “ParticleSeparation and Concentration System,” and co-pending, commonly assignedU.S. patent application Ser. No. 11/936,753, filed on Nov. 7, 2007,entitled “Device and Method for Dynamic Processing in WaterPurification,” and naming Lean et al. as inventors.

INCORPORATION BY REFERENCE

This application is related to co-pending, commonly assigned U.S. patentapplication Ser. No. 11/606,460, filed Nov. 30, 2006, entitled “ParticleSeparation and Concentration System,” and co-pending, commonly assignedU.S. patent application Ser. No. 11/936,753, filed on Nov. 7, 2007,entitled “Device and Method for Dynamic Processing in WaterPurification,” and naming Lean et al. as inventors which are bothincorporated herein by this reference in its entirety.

BACKGROUND

Conventional municipal water treatment (MWT) and other types of waterpurification systems include multi-stage filtration and sequentialprocess steps for coagulation, flocculation, and sedimentation. Aminimum of two stages of filtration typically include coarse 2-3 mm meshfilters at the inlet and 20-40 μm multi-media filters for finishing,although many utilities have more intermediate filtration steps.Neutrally buoyant particles (e.g. particles having substantially thesame density as water) can only be filtered or electro-chemicallymodified for sedimentation. Separation of these types of particles fromwater is very difficult. Moreover, such particles are typically TOC(total organic carbon) and contribute to major turbidity problems.

A spiral fluidic device useful for membrane-free filtration andseparation was described in U.S. application Ser. No. 11/606,460, filedNov. 30, 2006, entitled “Particle Separation and Concentration System,”which is incorporated herein by this reference in its entirely. Ingeneral, such devices are very useful in connection with particleshaving density differences compared with water, thus creatingcentrifugal or buoyancy forces necessary for transverse migrationthrough the channel for purposes of separation. However, neutrallybuoyant particles present a special case and thus require additionalfluidic considerations for separation. Heretofore, such additionalconsiderations have not been fully explored.

BRIEF DESCRIPTION

In one aspect of the presently described embodiments, the systemcomprises an inlet to receive at least a portion of the fluid containingthe neutrally buoyant particles, a spiral channel within which the fluidflows in a manner such that the neutrally buoyant particles flow in atubular band offset from a center of the channel, a first outlet for thefluid within which the tubular band flows, and, a second outlet for theremaining fluid or effluent.

In another aspect of the presently described embodiments, the inlet isangled to facilitate earlier formation of the tubular band along aninner wall of the spiral channel using a Coanda effect where wallfriction helps to attach impinging flow.

In another aspect of the presently described embodiments, the systemfurther comprises a second spiral channel nested with the spiral channelsuch that the tubular band is narrowed as a result of flowing throughthe second spiral channel.

In another aspect of the presently described embodiments, the systemfurther comprises a second inlet connected to the second outlet of thespiral channel to receive the remaining fluid, a second spiral channelwithin which the remaining fluid flows such that the remaining neutrallybuoyant particles flow in a second tubular band offset from the centerof the second channel, a third outlet for the fluid within which thesecond tubular band flows, and, a fourth outlet for more remainingfluid.

In another aspect of the presently described embodiments, the remainingneutrally buoyant particles are of a different size than the neutrallybuoyant particles output through the first outlet.

In another aspect of the presently described embodiments, the systemfurther comprises a second spiral channel within which at least anotherportion of the fluid flows.

In another aspect of the presently described embodiments, the systemfurther comprises a recirculation channel between the first outlet andthe inlet.

In another aspect of the presently described embodiments, the tubularband is formed as a function of at least one of fluid viscosity, averagechannel velocity, particle radius, fluid density, hydraulic diameter ofchannel, angular velocity, and differential velocity across particles.

In another aspect of the presently described embodiments, the tubularband is offset from the center of the channel as a function of a radiusof curvature of the spiral channel.

In another aspect of the presently described embodiments, the spiralchannel is a spiral wound structure.

In another aspect of the presently described embodiments, the spiralchannel is a helical spiral structure.

In another aspect of the presently described embodiments, the methodcomprises receiving at least a portion of the fluid containing theneutrally buoyant particles at an inlet, establishing a flow of thefluid in a spiral channel wherein the neutrally buoyant particles flowin a tubular band through the spiral channel in an asymmetric manner,outputting the fluid within which the tubular band flows through a firstoutlet of the channel, and, outputting the remaining fluid through asecond outlet of the spiral channel.

In another aspect of the presently described embodiments, the fluid isreceived at an angle to facilitate the formation of the tubular bandalong an inner wall of the spiral channel.

In another aspect of the presently described embodiments, the methodfurther comprises establishing a second flow of the fluid through asecond spiral channel nested with the spiral channel to narrow thetubular band.

In another aspect of the presently described embodiments, the methodfurther comprises establishing a flow of the remaining fluid in a secondspiral channel cascaded with the first spiral channel to separateneutrally buoyant particles of a different size than the neutrallybuoyant particles output through the first outlet.

In another aspect of the presently described embodiments, the methodfurther comprises establishing a flow of at least another portion offluid in a second spiral channel.

In another aspect of the presently described embodiments, the methodfurther comprises re-circulating in the system at least a portion of thefluid output through the first outlet.

In another aspect of the presently described embodiments, the flow ofneutrally buoyant particles in a tubular band is adjustable as afunction of fluid viscosity, average channel velocity, particle radius,fluid density, hydraulic diameter of the channel, angular velocity, anddifferential velocity across particles.

In another aspect of the presently described embodiments, the asymmetricmanner of flow of the tubular band is a function of a radius ofcurvature of the spiral channel.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a representation of a particle flowing through a channel andforces acting thereon;

FIGS. 2(a) and (b) illustrate a selected quantification of particleextraction;

FIGS. 3(a)-(f) illustrate an embodiment of a spiral device according tothe presently described embodiments;

FIG. 4 illustrates another embodiment according to the presentlydescribed embodiments;

FIG. 5 illustrates still another embodiment according to the presentlydescribed embodiments;

FIGS. 6(a) and (b) illustrate still further embodiments according to thepresently described embodiments;

FIGS. 7(a) and (b) illustrate still further embodiments according to thepresently described embodiments; and,

FIG. 8 illustrates a still further embodiment according to the presentlydescribed embodiments.

DETAILED DESCRIPTION

The presently described embodiments use a curved channel of a spiraldevice to introduce a centrifugal force upon neutrally buoyant particles(e.g., particles having substantially the same density as water, or thefluid in which the particles reside) flowing in a fluid, e.g. water, tofacilitate improved separation of such particles from the fluid. Asthese neutrally buoyant particles flow through the channel, a tubularpinch effect causes the particles to flow in a tubular band. Theintroduced centrifugal force perturbs the tubular band (e.g. forces thetubular band to flow in a manner offset from a center of the channel),resulting in an asymmetric inertial migration of the band toward theinner wall of the channel. This force balance allows for focusing andcompaction of suspended particulates into a narrow band for extraction.The separation principle contemplated herein implements a balance of thecentrifugal and fluidic forces to achieve asymmetric inertialequilibrium near the inner sidewall. Angled impingement of the inletstream towards the inner wall also allow for earlier band formation dueto a Coanda effect where wall friction is used to attach the impingingflow

The presently described embodiments relate to a membrane-free filtrationtechnology that is capable of continuous flow and high throughputoperation. The working principle relies primarily on purely fluidic flowin curved channel structures, eliminating the need for filter-interfacesor external force-fields. Balanced transverse force componentsconcentrate and divert particle streams according to the designed sizecut-off. This spiral flow filtration concept can address size and massbased separation of micro-particles, including biological agents. Thedesign simplicity makes this device amenable both to inline integrationwith other downstream processes and to serve as stand-alone,high-throughput, macro-scale or fine micro-scale lab-on-chipapplications.

With reference to FIG. 1, a curved channel 10 (e.g. a curved portion ofa spiral) having a particle 12 flowing there through is shown. As can beseen, asymmetric tubular pinch effects in the channel—created by variousforces—are shown. The forces include a lift force F_(W) from the innerwall, a Saffman force F_(S), Magnus forces F_(m) and a centrifugal forceF_(cf). It should be appreciated that the centrifugal force F_(cf) isgenerated as a function of the radius of curvature of the channel. Inthis regard, this added centrifugal force F_(cf) induces the slowsecondary flow or Dean vortex flow (shown by the dashed arrows) whichperturbs the symmetry of the regular tubular pinch effect. Particles areconcentrated in the inner equilibrium of the velocity contour (shown inthe dashed ellipses).

More specifically, fluidic shear in straight channels is known togenerate lateral forces which cause inertial migration of particulates.G. Segre and A. Silberberg, Nature, v. 189, p. 209 (1961), G. Segré andA. Silberberg, J. Fluid Mech., v. 14, p. 136 (1962), D. Leighton and A.Acrivos, Z. angew. Math. Phys., v. 36 p. 174 (1985), P. Cherukat, and J.B. McLaughlin, J. Fluid Mech., v. 263, p. 1 (1994), P. G. Saffman, J.Fluid Mech., v. 22, p. 385 (1965), S. I. Rubinow and J. B. Keller, J.Fluid Mech., v. 11, p. 447 (1961), B. P. Ho and L. G. Leal, J. FluidMech., v. 65, p. 365 (1974), P. Vasseur and R. G. Cox, J. Fluid Mech.,v. 78, p. 385 (1976), J. Feng, H. H. Hu and D. D. Joseph, J. FluidMech., v. 277, p. 271 (1994), E. Ashmolov, J. Fluid Mech., v. 381, p. 63(1999), E. Ashmolov, Phys. Fluids, v. 14, p. 15 (2002), J.-P. Matas, J.F. Morris and É. Guazzelli, J. Fluid Mech., v. 515, p. 171 (2004), B. H.Yang, J. Wang, D. D. Joseph, H. H. Hu, T.-W. Pan and R. Glowinski, J.Fluid Mech., v. 540, p. 109 (2005), E. E. Michaelides, J. Fluids Eng.,v. 125, p. 209, (2003), P. Cherukat and J. B. McLaughlin, Int. J.Multiphase Flow, v. 16, p. 899 (1990), P. Cherukat, J. B. McLaughlin andA. L. Graham, Int. J. Multiphase Flow, v. 20, p. 339 (1994).

G. Segré and A. Silberberg, Nature, v. 189, p. 209 (1961), and G. Segréand A. Silberberg, J. Fluid Mech., v. 14, p. 136 (1962), experimentallydemonstrated a tubular pinch effect where neutrally buoyant particlesmigrate to form a symmetric band that is 0.6 D wide, where D is thechannel diameter. In quadratic Poiseuille flow, three contributions haveexplained the lateral migration of a rigid sphere. The wall lift, F_(W),acts to repel particulates from the wall due to lubrication. D. Leightonand A. Acrivos, Z. angew. Math. Phys., v. 36 p. 174 (1985), P. Cherukat,and J. B. McLaughlin, J. Fluid Mech., v. 263, p. 1 (1994). The secondcontribution is the Saffman inertial lift, F_(S), towards the wall dueto shear slip,F _(s)=6.46ηVaR _(e) ^(1/2)  (1)

where η, V, a, and Re are respectively, the fluid viscosity, averagechannel velocity, particle radius, and channel Reynold's number givenby:R _(e) =ρVD/η  (2)

with ρ and D being the fluid density and hydraulic diameter of thechannel. [10, 14]. The third is the Magnus force, F_(m), due to particlerotation towards the wall,F _(m) =πa ³ ρ{right arrow over (Ω)}×{right arrow over (V)}  (3)

where Ω_(r) is the angular velocity given by ΔV/r and ΔV is thedifferential velocity across the particle S. I. Rubinow and J. B.Keller, J. Fluid Mech., v. 11, p. 447 (1961). F_(w) dominates near thewall and achieves equilibrium with the combined effects of F_(s) andF_(m) to confine particles in a band. G. Segre and A. Silberberg, J.Fluid Mech., v. 14, p. 136 (1962), developed a reduced length parameterto scale this tubular pinch effect in a simple form,

$\begin{matrix}{L = {\left( \frac{\rho\;{Vl}}{\eta} \right)\left( \frac{a}{d} \right)^{3}}} & (4)\end{matrix}$

where l is the actual channel length and d is the hydraulic channelradius. In curvilinear channel geometry, a centrifugal force, F_(cf),modifies the symmetric tubular pinch effect. The fluid inertia from thisforce causes a secondary transverse flow or Dean vortex, P. Cherukat andJ. B. McLaughlin, Int. J. Multiphase Flow, v. 16, p. 899 (1990), P.Cherukat, J. B. McLaughlin and A. L. Graham, Int. J. Multiphase Flow, v.20, p. 339 (1994), S. A. Berger, L. Talbot and L.-S. Yao, Ann. Rev.Fluid Mech., v. 15, p. 461 (1983), Yu. P. Gupalo, Yu. V. Martynov andYu. S. Ryazantsev, Fluid Dyn., 12, 109 (1977) which is a doublerecirculation as shown by the dot arrows in FIG. 1. The Dean number is ameasure of the strength of this recirculation:D _(e)=2(d/R)^(1/2) R _(e)  (5)

where R is the radius of curvature of the channel S. A. Berger, L.Talbot and L.-S. Yao, Ann. Rev. Fluid Mech., v. 15, p. 461 (1983).Particles in mid-elevation migrate transversely outward with the Deanvortex, are repelled by the wall lift, and continue to loop back alongthe top and bottom walls towards the inside wall. The combined Saffmanand Magnus forces are large in comparison to the viscous drag of theDean vortex so particles are trapped in a force minimum located adjacentand closer to the inner wall.

So, it is apparent that the contemplated tubular band is formed as afunction of at least one of fluid viscosity, average channel velocity,particle radius, fluid density, hydraulic diameter of channel, angularvelocity, and differential velocity across particles. Moreover, as notedabove, the tubular band is offset from the center of the channel as afunction of a radius of curvature of the spiral channel. So, theconfiguration and operation of the system is a function of the factorscontemplated, for example, by Equation 4. These factors or parametersare highly scalable and will vary as a matter of application in therange from micro-scale devices to macro-scale devices. Examples areprovided herein; however, other implementations are contemplated.

Implementation of the methodology described herein results in a systemwhereby particles can be separated within a spiral channel and output ina manner so as to separate particles of selected sizes from an effluentstream. For example, with reference to FIG. 2, a Coulter counterquantification of such particle extraction is illustrated. At 92 mm/sflow velocity, the concentration ratio of extracted particles in aparticulate band 20, as shown in FIG. 2(b), is 300 times that of theeffluent 22 that is being output by the spiral channel 24.Experimentally, this calculates to a 99.1% efficiency of particleremoval using the presently described embodiments.

Other advantages of the presently described embodiments include:

1) Filtration capacity such as sample, volume, hydraulic retentiontimes, filtration rate, cut-off particle size, and concentration factorcan be adjusted by tailoring fluidic and dimensional parameters.

2) Extension to size separation would merely involve tailoring of theflow parameters for a monotonic range of particle sizes and providingcapture channels in sequential manner along the spiral channel.

3) Ability to cascade several of these spiral structures, each tailoredfor a decreasing particle size range cut-off.

4) Design simplicity making this device amenable both to inlineintegration with other downstream processes and to serve as astand-alone application.

5) Large dynamic size range in its filtration capacity makes it suitedfor both high-throughput macroscale and fine micro-scale lab-on-chipapplications.

6) Parallelization of modular units can be realized for higherthroughput.

7) This membrane-free device has the desirable combinations ofhigh-throughput and low cost, making it inherently suited forpreparative filtration in the range of micro-scale to macro-scaleapplications.

8) Design technique is provided for a spiral structure for rapid fluidicseparation of neutrally buoyant particles without a membrane.

9) Double nested spiral channels can be implemented to compact bandsuccessively from both sides.

10) Highly scalable implementation based on reduced length formula isrealized.

11) Flocculation and sedimentation steps can be eliminated inconventional water treatment.

12) Contemplated structures may be used for other applications in waterincluding: IC fab reclaim, cooling tower water, MBR (membrane bioreactor), pre-treatment for RO (reverse osmosis).

It should be appreciated that these advantages may be achieved in avariety of different embodiments. These embodiments will vary as afunction of the parameters noted above which are controllable and/orconfigurable through channel design and operational parameters.Nonetheless, the described systems generally include an inlet to receiveat least a portion of the fluid containing the neutrally buoyantparticles, a spiral channel within which the fluid flows in a mannersuch that the neutrally buoyant particles flow in a tubular band offsetfrom a center of the channel, a first outlet for the fluid within whichthe tubular band flows and a second outlet for the remaining fluid. So,in operation, the method includes receiving at least a portion of thefluid containing the neutrally buoyant particles at an inlet,establishing a flow of the fluid in a spiral channel wherein theneutrally buoyant particles flow in a tubular band through the spiralchannel in an asymmetric manner, outputting the fluid within which thetubular band flows through a first outlet of the channel and outputtingthe remaining fluid through a second outlet of the spiral channel.

In this regard, FIG. 3(a) illustrates a spiral structure 30 that may beimplemented in accordance with the presently described embodiments. Thisstructure 30 is a double nested structure wherein a first spiral channelis nested with a second spiral channel. That is, the inlet 32 isconnected to a spiral channel that spirals to the center of thestructure 30 and then spirals back out to the outer periphery of thestructure 30—without interruption other than a change in direction. So,the outlet 34, having a first outlet portion 36 and a second outletportion 38, is disposed on the outer periphery, as opposed to the centerof the structure 30.

It should also be appreciated that the inlet could provide for an angledor inclined entry of fluid to the system to facilitate quicker formationof the tubular band along an inner wall of the spiral channel. This isthe result of the Coanda effect where wall friction is used to attachthe impinging flow. With reference to FIG. 8, the channel 10 has aninlet 11 wherein the inlet stream is angled toward the inner wall by anangle θ. The tubular band 18 is thus formed earlier for egress out ofthe outlet 14. Of course, the second outlet 16 for the remaining fluidin which the band 18 does not flow is also shown. It should beunderstood that the inlet angle may be realized using any suitablemechanism or technique.

With reference back now to FIG. 3(a) according to the presentlydescribed embodiments, the noted lateral forces across the spiralchannel geometry transform a relatively homogeneous distribution ofparticles at the inlet 32 into an ordered band at the outlet 34. Afterspiral circulation, particles are collected at an inside outlet 36 andthe effluent (water) are collected at an outside outlet 38.

Sequential images along the fluidic path are shown. Images are rotatedand mirrored to match their flow directions for comparison. The bottomsides are toward the center of the spirals. The fluid runs left to rightor bottom to top at the mean fluidic velocity of 92 mm/s. As shown, adispersed particle suspension was introduced into an inlet (P#1) (FIG.3(b)) with an average flow velocity of 92 mm/s. After two spiral turns(P#2) (FIG. 3(c)), the particles closest to the inner wall (lowerboundary) have started to concentrate at 0.6w from the channel centerwhere w is a half of the channel width. At the transitional point after12 turns (P#3) (FIG. 3(d)), particle concentration shows a band with asharp edge on the inside and a more diffuse edge on the outside. Itshould be noted that this (P#3) (FIG. 3(d)) is a transition point tochange the flow from clockwise to counter-clockwise direction. Thistransition has beneficial effects on compacting the band of particles.After the transition point, the sharp edge of the band is switched tothe outside and the continuing lateral force acts to mitigate againstthe dispersive effects of Brownian motion and diffusion. On the otherhand, the diffuse outside edge of the band is switched to the inside andis now subjected to the compacting effect of the centrifugal and liftforce induced effect. As a result, a sharp edge is developed as observed(P#4) (FIG. 3(e)). The concentrated band of particles are diverted intothe inside outlet (P#5, L=34.2) (FIG. 3(f)) whilst the effluent streamis routed into the outside outlet. Segre and Silberberg showed that thereduced length parameter for one order of concentration differenceshould be L>9 G. Segré and A. Silberberg, J. Fluid Mech., c. 14, p. 136(1962). The concentration difference between the collected samples isexpected be about two orders of magnitude. The resultant band is lessthan 0.2 D wide and could be further compacted.

Particle counting of collected samples after filtration confirm theresults from the preceding observation. After the samples were filteredwith different flow rates, the collected samples were diluted to 50times for coulter counting (Z2™ COULTER COUNTER®, Beckman Coulter,Calif., USA). The concentration of particles from the outer outletdecreased as the flow velocity increased. As discussed previously, theefficiency of filtration depends on the corresponding length L that is afunction of (particle velocity). Faster flow velocity improvedfiltration efficiency (particle capture efficiency) from 64.7% at 23mm/s to 99.1% at 92 mm/s. The separation factor or ratio ofconcentrations of the particle and effluent outlets exceeds 300×, andcan be further optimized. The important effect of the spiral geometry isto focus the particles into a narrow band through the asymmetric tubularpinch effect. This nested double spiral (FIG. 3(a)) acts to sequentiallycompact each side of the band resulting in a sharper and narrower bandthan is predicted by the tubular pinch effect alone.

In another embodiment, FIG. 4 illustrates the implementation of a spiralseparator device according to the presently described embodiments withina purification system 400. As shown, the system includes a screen 402, aflash mixer 405, and a reduced coagulation tank 404. The spiral device408 according to the presently described embodiments includes an inlet410 as well as a first outlet 412 and a second outlet 414. Also shown inthe system 400 is a recirculation channel or path 416 which is disposedbetween the inlet 410 and the coagulation tank 404.

In operation, fluid containing neutrally buoyant particles is receivedin the system and first filtered through the screen 402. The filteredwater is then flash-mixed 405 before being introduced into the spiraldevice 408 through inlet 410. As the fluid flows in the spiral device408, the tubular band of neutrally buoyant particles is maintained toflow in an asymmetric manner, relative to the center of the channel.This asymmetry allows for convenient separation of the fluid withinwhich the tubular band flows (which is output through outlet 412) andthe remaining fluid (which is output through outlet 414). Theconcentrate stream is optionally re-circulated back, for example, to thereduced coagulation tank from outlet 412 to increase water recovery.

With reference now to FIG. 5, a further embodiment to the presentlydescribed embodiments is shown. In this embodiment, a purificationsystem 500 includes a two-stage spiral separation system to isolateparticles of different sizes. In the example system shown, the particlesare isolated in a 1 to 10 micrometer range. As shown, the systemincludes an input water source 502 connecting to a spiral separator 504having an inlet 506, as well as a first outlet 508 and a second outlet510. The second outlet 510 is connected to a second spiral separator 520by way of an inlet 522. The spiral separator 520 includes a first outlet524 and a second outlet 526 as shown.

In operation, the system 500 with the cascaded spiral stages facilitatesa first separation of particles between those of greater than 10micrometers being output from the first spiral separator in a wastestream and particles less than 10 micrometers being input to the secondspiral separator 520 for further processing. The second spiral separatorthen separates particles greater than 1 micrometer and outputs fluidwithin which those particles reside by way of outlet 524. The remainingfluid or effluent is output through outlet 526. In this manner, thesystem 500 is able to isolate particles between 1 and 10 micrometers forvarious sampling processing. This concept can be extended by continuedcascading of spiral structures with smaller size cut-offs to achievefractionation of particles with decreasing size ranges.

With reference now to FIGS. 6 (a) and (b), a still further embodiment isshown. In FIG. 6, a spiral device 600 according to the presentlydescribed embodiments is illustrated. In this embodiment, the spiraldevice 600 takes the form of a helical spiral. In this regard, thespiral body portion of the device 604 is a helical spiral that has aninlet 606, a first outlet 608 and a second outlet 610. As shown in FIG.6(b), a spiral device such as that shown in FIG. 6(a) can be disposed ina parallel arrangement to increase throughput of the system. As shown,spiral devices 600 are all connected to an input main 620 from a fluidmanifold and the respective first outlets of the devices 600 areconnected to a first outlet main 622. The second outlets of the devices600 are connected to a second outlet main 624.

With reference to FIGS. 7(a) through 7(b), a similar system is shown.However, the embodiment of FIG. 7(a) shows a spiral device 700 that is aspiral wound device. This device 700 includes a spirally wound body 704having inlet 706, a first outlet 708 and a second outlet 710. As withthe embodiment illustrated in FIGS. 6(a) and 6(b), the device 700, asshown in FIG. 7(b), may be disposed in a system wherein a plurality ofdevices 700 are connected in parallel to a water inlet main 720 from afluid manifold. Similarly, the first outlet lines for the devices areconnected to a first outlet main 722. The second outlet lines of thedevices 700 are connected to a second outlet main 724.

It should be appreciated that the spiral devices contemplated herein maytake a variety of forms including the form of any of the spiral devicesdescribed in connection with co-pending and commonly assigned U.S.application Ser. No. 11/606,460, filed Nov. 30, 2006, entitled “ParticleSeparation and Concentration System”, which is incorporated herein inits entirety by this reference, provided that such devices areconfigured, dimensioned and operated to advantageously address neutrallybuoyant particles within fluid. Of course, appropriate modificationswould be made to such devices to accommodate the presently describedembodiments. Moreover, it should be appreciated that any of the spiraldevices described or contemplated herein may be disposed in a cascadedmanner, as shown in FIG. 5, or in a parallel manner, as shown in FIGS.6(a), 6(b), 7(a) and 7(b). Still further, any suitable material may beused to form the spiral devices contemplated herein.

It will be appreciated that various of the above-disclosed and otherfeatures and functions, or alternatives thereof, may be desirablycombined into many other different systems or applications. Also thatvarious presently unforeseen or unanticipated alternatives,modifications, variations or improvements therein may be subsequentlymade by those skilled in the art which are also intended to beencompassed by the following claims.

The invention claimed is:
 1. A system for separation of neutrallybuoyant particles from a fluid, the system comprising: an inlet toreceive at least a portion of the fluid containing the neutrally buoyantparticles; a spiral channel having a curvilinear channel geometrytailored to form in the fluid a tubular band having the neutrallybuoyant particles flowing therein, the tubular band flow being throughthe channel in an asymmetric manner based on a balance of forces andinducement of a Dean vortex flow, wherein the flow of neutrally buoyantparticles in the tubular band is a function of fluid viscosity, averagechannel velocity, particle radius, fluid density, hydraulic diameter ofthe channel, angular velocity, and differential velocity acrossparticles; a first outlet for the fluid within which the tubular bandflows; and, a second outlet for the remaining fluid.
 2. The system asset forth in claim 1 wherein the inlet is angled to facilitate earlierformation of the tubular band along an inner wall of the spiral channel.3. The system as set forth in claim 1 further comprising a second spiralchannel nested with the spiral channel such that the tubular band isnarrowed as a result of flowing through the second spiral channel. 4.The system as set forth in claim 1 further comprising: a second inletconnected to the second outlet of the spiral channel to receive theremaining fluid; a second spiral channel within which the remainingfluid flows such that the remaining neutrally buoyant particles flow ina second tubular band offset from the center of the second channel; athird outlet for the fluid within which the second tubular band flows;and, a fourth outlet for more remaining fluid.
 5. The system as setforth in claim 4 wherein the remaining neutrally buoyant particles areof a different size than the neutrally buoyant particles output throughthe first outlet.
 6. The system as set forth in claim 1 furthercomprising a second spiral channel within which at least another portionof the fluid flows.
 7. The system as set forth in claim 1 furthercomprising a recirculation channel between the first outlet and theinlet.
 8. The system as set forth in claim 1 wherein the asymmetricmanner of flow of the tubular band is a function of a radius ofcurvature of the spiral channel.
 9. The system as set forth in claim 1wherein the spiral channel is a spiral wound structure.
 10. The systemas set forth in claim 1 wherein the spiral channel is a helical spiralstructure.
 11. A method for separating neutrally buoyant particles froma fluid, the method comprising: receiving at least a portion of thefluid containing the neutrally buoyant particles at an inlet;establishing a flow of the fluid in a spiral channel tailored togenerate a tubular band in the fluid having the neutrally buoyantparticles flowing therein, the tubular band flowing through the spiralchannel in an asymmetric manner based on a balance of forces andinducement of a Dean vortex flow, the flow of neutrally buoyantparticles in the tubular band being adjustable as a function of fluidviscosity, average channel velocity, particle radius, fluid density,hydraulic diameter of the channel, angular velocity, and differentialvelocity across particles; outputting the fluid within which the tubularband flows through a first outlet of the channel; and, outputting theremaining fluid through a second outlet of the spiral channel.
 12. Themethod as set forth in claim 11 wherein the fluid is received at anangle to facilitate the formation of the tubular band along an innerwall of the spiral channel.
 13. The method as set forth in claim 11further comprising establishing a second flow of the fluid through asecond spiral channel nested with the spiral channel to narrow thetubular band.
 14. The method as set forth in claim 13 further comprisingestablishing a flow of the remaining fluid in a second spiral channelcascaded with the first spiral channel to separate neutrally buoyantparticles of a different size than the neutrally buoyant particlesoutput through the first outlet.
 15. The method as set forth in claim 11further comprising establishing a flow of at least another portion offluid in a second spiral channel.
 16. The method as set forth in claim11 further comprising re-circulating in the system at least a portion ofthe fluid output through the first outlet.
 17. The method as set forthin claim 11 wherein establishing the asymmetric manner of flow of thetubular band is a function of a radius of curvature of the spiralchannel.
 18. A system for separation of neutrally buoyant particles froma fluid, the system comprising: an inlet to receive at least a portionof the fluid containing the neutrally buoyant particles; a curvedchannel having a curvilinear channel geometry tailored to form in thefluid a tubular band having the neutrally buoyant particles flowingtherein, the tubular band flow being through the channel in anasymmetric manner based on a balance of forces and inducement of a Deanvortex flow, wherein the flow of neutrally buoyant particles in thetubular band is a function of fluid viscosity, average channel velocity,particle radius, fluid density, hydraulic diameter of the channel,angular velocity, and differential velocity across particles; a firstoutlet for the fluid within which the tubular band flows; and, a secondoutlet for the remaining fluid.
 19. A system comprising: fluid havingneutrally buoyant particles therein; an inlet to receive at least aportion of the fluid containing the neutrally buoyant particles; acurved channel having a tailored curvilinear channel geometry causingfluid flows such that the neutrally buoyant particles flow in a tubularband, the tubular band flow being through the channel in an asymmetricmanner based on a balance of forces and inducement of a Dean vortexflow, wherein the flow of neutrally buoyant particles in the tubularband is a function of fluid viscosity, average channel velocity,particle radius, fluid density, hydraulic diameter of the channel,angular velocity, and differential velocity across particles; a firstoutlet for the fluid within which the tubular band flows; and, a secondoutlet for the remaining fluid.
 20. A method for separating neutrallybuoyant particles from a fluid, the method comprising: receiving atleast a portion of the fluid containing the neutrally buoyant particlesat an inlet; establishing a flow of the fluid in a curved channeltailored to generate a tubular band in the fluid having the neutrallybuoyant particles flowing therein, the tubular band flowing through thechannel in an asymmetric manner based on a balance of forces andinducement of a Dean vortex flow, the flow of neutrally buoyantparticles in the tubular band being adjustable as a function of fluidviscosity, average channel velocity, particle radius, fluid density,hydraulic diameter of the channel, angular velocity, and differentialvelocity across particles; outputting the fluid within which the tubularband flows through a first outlet of the channel; and, outputting theremaining fluid through a second outlet of the channel.
 21. A method forseparating neutrally buoyant particles from a fluid, the methodcomprising: receiving at least a portion of the fluid containing theneutrally buoyant particles at an inlet; establishing a flow of thefluid in a spiral channel tailored to generate a tubular band in thefluid having the neutrally buoyant particles flowing therein, thetubular band flowing through the spiral channel in an asymmetric manner;adjusting the flow of neutrally buoyant particles in the tubular band asa function of fluid viscosity, average channel velocity, particleradius, fluid density, hydraulic diameter of the channel, angularvelocity, and differential velocity across particles; outputting thefluid within which the tubular band flows through a first outlet of thechannel; and, outputting the remaining fluid through a second outlet ofthe spiral channel.
 22. A method for separating neutrally buoyantparticles from a fluid, the method comprising: receiving at least aportion of the fluid containing the neutrally buoyant particles at aninlet; establishing a flow of the fluid in a curved channel tailored togenerate a tubular band in the fluid having the neutrally buoyantparticles flowing therein, the tubular band flowing through the channelin an asymmetric manner; adjusting the flow of neutrally buoyantparticles in the tubular band as a function of fluid viscosity, averagechannel velocity, particle radius, fluid density, hydraulic diameter ofthe channel, angular velocity, and differential velocity acrossparticles; outputting the fluid within which the tubular band flowsthrough a first outlet of the channel; and, outputting the remainingfluid through a second outlet of the channel.
 23. The system as setforth in claim 18 wherein the asymmetric manner of flow of the tubularband is a function of a radius of curvature of the channel.
 24. Thesystem as set forth in claim 19 wherein the asymmetric manner of flow ofthe tubular band is a function of a radius of curvature of the channel.